1. Field of the Invention
The invention is directed to an improved fuel injection system for an internal combustion engine.
2. Description of the Prior Art
One fuel injection system of the type with which this invention is concerned, known from German Patent Disclosure DE 39 00 763 A1, has a high-pressure fuel pump and a fuel injection valve for each cylinder of the engine. The high-pressure fuel pump has an engine-driven pump piston defining a pump work chamber, and a communication of the pump work chamber with a relief chamber is controlled by an electrically controlled valve. The fuel injection valve has an injection valve member, by which at least one injection opening is controlled, and which is movable in an opening direction, counter to the force of a closing spring disposed in a spring chamber, by the pressure prevailing in a pressure chamber that communicates with the pump work chamber. The closing spring is braced on one end at least indirectly on the injection valve member and on the other at least Indirectly on a storage piston. The storage piston, on its side remote from the closing spring, is subjected to the pressure prevailing in the pump work chamber and is movable in a stroke motion counter to the force of the closing spring. The storage piston is movable from an outset position, at low pressure in the pressure chamber, into the storage chamber, and the deflection stroke motion of the storage piston into the storage chamber is limited by a stop. The storage piston has a shaft part, which is disposed in a connecting bore between the storage chamber and the spring chamber and protrudes into the spring chamber. Upon the deflection stroke motion of the storage piston, fuel is positively displaced by the storage piston from the storage chamber into the spring chamber through a gap that is present between the shaft part and the connecting bore. As a result, damping of the stroke motion of the storage piston is accomplished. The damping of the motion of the storage piston can either be constant over the stroke of the storage piston or such that the damping is strong at the onset of the deflection stroke motion and then decreases. It has been found that the damping attained in this way is insufficient, and thus the storage piston strikes the stop at high speed, causing irritating noises.
The fuel injection system of the invention has the advantage over the prior art that because of how the shaft part is embodied, with the shaft portion of smaller cross section disposed in the connecting bore in the outset position of the storage piston and the shaft portion of larger cross section dipping into the connecting bore upon the deflection stroke motion, the damping is less of the motion of the storage piston at the onset of the deflection stroke motion and is stronger as the deflection stroke motion increases, so that the storage piston strikes the stop at only slight speed, causing only reduced irritating noise, if any.
Other advantageous features and refinements of the fuel injection system of the invention are disclosed. In one embodiment using a support element of the requisite strength; makes simple adjustment of the position of the shaft part relative to the storage piston possible. Another embodiment makes the adjustment of the position of the shaft part possible by using balls of different diameter, which are available as standardized components in various finely graduated diameters. A further embodiment makes it possible for stronger damping to become effective only after a partial deflection stroke of the storage piston.